1. Field of the Invention
The present invention generally relates to communications over packet networks, such as Internet Protocol (“IP”) and, more particularly, to connecting communication devices over IP, such as connecting modem devices over IP.
2. Related Art
Today the traditional analog telephony is being rapidly replaced with digital IP telephony, which use various techniques to break voice into data packets for transmission over packet networks. Analog modems have been utilized to provide data, facsimile and voice communications over twisted pair telephone lines for decades. Modem is an analog-to-digital and digital-to-analog converter, which is capable of adapting a terminal or computer to an analog telephone line by converting digital pulses to audio frequencies and vice versa. Because a significant infrastructure is in place using such modems, the packet networks need to address and support modem communication.
FIG. 1 illustrates a block diagram of a conventional communications network 100 utilizing modems for communication over a packet network protocol, such as Internet Protocol, which may also be referred to as Modem over Internet Protocol (“MoIP”). As shown, communications network 100 includes first communication device 102 in communication with first gateway device 104 and second gateway device 114 in communication with second communication device 122. Communications network 100 further includes a packet network protocol, such as IP 112 to provide communications between first gateway device 104 and second gateway device 114. IP 112 implements the network layer (layer 3) of a network protocol, which contains a network address and is used to route a message to a different network or subnetwork. IP 112 accepts packets from the layer 4 transport protocol, such as Transmission Control Protocol (“TCP”) or User Data Protocol (“UDP”), and adds its own header and delivers the data to the layer 2 data link protocol. TCP provides transport functions, which ensures that the total amount of bytes sent is received correctly at the other end. UDP, which is part of the TCP/IP suite, is an alternate transport that does not guarantee delivery. UDP is widely used for real-time voice and video transmissions where erroneous packets are not retransmitted.
Devices 102, 104, 114 and 122 may include modems (modulator-demodulator). Modems may support a variety of data modulation standards, such as ITU (International Telecommunications Union) standards: V.22bis, V.34, V.90 or V.92, etc. Typically, modems have built-in error correction, such as MNP2-4 or LAPM (or V.42) and data compression, such as MNP5, V.42bis or V.44. Modems are also capable of supporting various voice and facsimile standards.
The communication process begins when first communication device 102, e.g. first modem (“M1”), originates a call to establish communications with second communication device 122, e.g. second modem (“M2”). First gateway device 104 (“G1”) receives the call and informs second gateway device 114 (“G2”) of the call for M2 over communications network 100 and, as a result, G2 calls M2.
Typically, in the default mode of operation, G1 and G2 communicate in voice mode and use compressed voice protocol, such as the ITU standard G.723. Conventionally, after M2 receives the call from G2, M2 answers the call and starts sending certain defined initiating signals, such as an answer tone, which is typically transmitted at about 2100 Hz frequency. At this point, G2 starts confirming the answer tone for a pre-defined period of time, e.g. 50 ms to 1000 ms. Once G2 confirms the answer tone, G2 informs G1 that the present communication session is a modem or facsimile session.
However, once G2 detects the answer tone, e.g., 2100 Hz tone, from M2, then G2 and G1 switch to an uncompressed voice protocol, such as an ITU standard G.711, which provides toll quality audio at 64 Kbps using either A-Law or mu-Law pulse code modulation methods. This uncompressed digital format is used in order to allow easy connections to legacy telephone networks. By switching to G.711, the signals generated by M2 may propagate through from G2 to G1 in a more intact manner in order to reach the first modem at the other side, which is known as modem pass through mode of MoIP. Alternatively, once G2 detects the answer tone from M2, then G1 and G2 may switch into other modes designed to accommodate modem or facsimile devices, such as terminating M1–G1 call and M2–G2 call locally, which is known as modem relay mode of MoIP. The present application hereby incorporates by reference two recent ITU Recommendations, for MoIP, referred to as V.150.0 and V.150.1.
However, there are many drawbacks in the above-described method and system of connecting communication devices, such as modems and facsimile devices over IP. As described above, prior to switching out of compressed voice mode, e.g. G.729 or G.723 to uncompressed voice mode, such as G.711, or to modem or facsimile mode, G2 must confirm presence of answer tone that is being generated by M2 for a sufficient period of time. In other words, all signals that are generated by M2 prior to the generation of the answer tone by M2 are simply passed along by G2 over the packet network to G1 and M1. One set of such signals that may be generated by some modems, such as K56 modems, prior to the answer tone is known as V.8bis signals, which are used to exchange and select modes of operation between modems. V.8bis is an International Telecommunication Union standard, entitled “Procedures for Identification and Selection of Common Modes of Operation Between Data Circuit Terminating Equipments (DCEs) and between Data Terminal Equipments (DTEs) over the Public Switched Telephone Network and on Leased Point-To-Point Telephone Type Circuits”, dated November 2000, which is hereby incorporated by reference.
One specific problem occurs in modem relay when M1 and M2 engage in transacting V.8bis signals to exchange modes of operation and select modes of operation prior to configuration of G1 and G2 for modem over IP operation to terminate M1–G1 and M2–G2 connections locally to facilitate a modem relay. For example, in modem relay, end-to-end V.8bis negotiations between M1 and M2 must be blocked, so V.8bis negotiations can occur locally between M1–G1 and M2–G2. If M1 and M2 start negotiating V.8bis capabilities end-to-end, local V.8bis negotiations between M1-G1 and M2 and G2 can no longer be performed and the local connections may fail or fallback to undesirably low speed connections.
Another specific problem occurs in modem pass through when M1 and M2 engage in transacting V.8bis signals to exchange modes of operation and select modes of operation prior to G1 and G2 being configured for modem pass through mode, e.g. switching from G.723.1 to G.711, reconfiguring jitter buffers, disabling echo cancellers, etc. In the event that G1 and G2 are not configured timely for modem pass through mode, modem signals may not be exchanged end-to-end between M1 and M2 in an intact manner due to the interferences caused by G1 and G2 voice configuration, and M1 and M2 connection may either fail or fallback to undesirably low speed connection.
Accordingly, there is an intense need in the art for communication networks utilizing a packet network protocol that are able to efficiently, reliably and timely detect and handle modems that support V.8bis.